diff --git a/Makefile b/Makefile
index 43de3a7..f5b9d5f 100644
--- a/Makefile
+++ b/Makefile
@@ -64,7 +64,7 @@ mspdebug: main.o fet.o rf2500.o dis.o uif.o olimex.o ihex.o elf32.o stab.o \
 	  reader.o vector.o output_util.o expr.o fet_error.o binfile.o \
 	  fet_db.o usbutil.o titext.o srec.o device.o coff.o opdb.o output.o \
 	  cmddb.o stdcmd.o prog.o flash_bsl.o list.o simio.o simio_tracer.o \
-	  simio_timer.o
+	  simio_timer.o simio_wdt.o
 	$(CC) $(LDFLAGS) $(PORTS_LDFLAGS) -o $@ $^ -lusb $(READLINE_LIBS)
 
 .c.o:
diff --git a/mspdebug.man b/mspdebug.man
index c318a78..45f64f1 100644
--- a/mspdebug.man
+++ b/mspdebug.man
@@ -503,6 +503,23 @@ Clear a signalled interrupt request.
 Reset the clock cycle and instruction counts to 0, and clear the IO event
 history.
 .RE
+.IP "\fBwdt\fR"
+This peripheral simulates the Watchdog Timer+, which can be used in software
+either as a watchdog or as an interval timer. It has no constructor arguments.
+
+The simulated state of the NMI/RST# pin can be controlled through a configuration
+parameter. Note that if this pin state is held low with the pin mode selected
+as a reset (the default), the CPU will not run.
+
+The extended information for this peripheral shows all register states, including
+the hidden counter register. Configuration parameters are:
+.RS
+.IP "\fBnmi\fR \fIstate\fR"
+Set the NMI/RST# pin state. The argument should be zero to indicate a low state
+or non-zero for a high state.
+.IP "\fBirq\fR \fIirq\fR"
+Select the interrupt vector for interval timer mode. The default is to use
+interrupt vector 10.
 .SH ADDRESS EXPRESSIONS
 Any command which accepts a memory address, length or register value
 as an argument may be given an address expression. An address
diff --git a/sim.c b/sim.c
index cb2cb83..a49e139 100644
--- a/sim.c
+++ b/sim.c
@@ -490,6 +490,15 @@ static int step_cpu(struct sim_device *dev)
 	return ret;
 }
 
+static void do_reset(struct sim_device *dev)
+{
+	simio_step(dev->regs[MSP430_REG_SR], 4);
+	memset(dev->regs, 0, sizeof(dev->regs));
+	dev->regs[MSP430_REG_PC] = MEM_GETW(dev, 0xfffe);
+	dev->regs[MSP430_REG_SR] = 0;
+	simio_reset();
+}
+
 static int step_system(struct sim_device *dev)
 {
 	int count = 1;
@@ -497,7 +506,10 @@ static int step_system(struct sim_device *dev)
 	uint16_t status = dev->regs[MSP430_REG_SR];
 
 	irq = simio_check_interrupt();
-	if (((status & MSP430_SR_GIE) && irq >= 0) || irq >= 14) {
+	if (irq == 15) {
+		do_reset(dev);
+		return 0;
+	} else if (((status & MSP430_SR_GIE) && irq >= 0) || irq >= 14) {
 		if (irq >= 16) {
 			printc_err("sim: invalid interrupt number: %d\n", irq);
 			return -1;
@@ -631,11 +643,7 @@ static int sim_ctl(device_t dev_base, device_ctl_t op)
 
 	switch (op) {
 	case DEVICE_CTL_RESET:
-		simio_step(dev->regs[MSP430_REG_SR], 4);
-		memset(dev->regs, 0, sizeof(dev->regs));
-		dev->regs[MSP430_REG_PC] = MEM_GETW(dev, 0xfffe);
-		dev->regs[MSP430_REG_SR] = 0;
-		simio_reset();
+		do_reset(dev);
 		return 0;
 
 	case DEVICE_CTL_HALT:
diff --git a/simio.c b/simio.c
index 30aa704..f2fc750 100644
--- a/simio.c
+++ b/simio.c
@@ -26,10 +26,12 @@
 
 #include "simio_tracer.h"
 #include "simio_timer.h"
+#include "simio_wdt.h"
 
 static const struct simio_class *const class_db[] = {
 	&simio_tracer,
-	&simio_timer
+	&simio_timer,
+	&simio_wdt
 };
 
 /* Simulator data. We keep a list of devices on the bus, and the special
@@ -316,8 +318,28 @@ int name(address_t addr, datatype data) { \
 
 IO_REQUEST_FUNC(simio_write, write, uint16_t)
 IO_REQUEST_FUNC(simio_read, read, uint16_t *)
-IO_REQUEST_FUNC(simio_write_b, write_b, uint8_t)
-IO_REQUEST_FUNC(simio_read_b, read_b, uint8_t *)
+IO_REQUEST_FUNC(static simio_write_b_device, write_b, uint8_t)
+IO_REQUEST_FUNC(static simio_read_b_device, read_b, uint8_t *)
+
+int simio_write_b(address_t addr, uint8_t data)
+{
+	if (addr >= 0 && addr < 16) {
+		sfr_data[addr] = data;
+		return 0;
+	}
+
+	return simio_write_b_device(addr, data);
+}
+
+int simio_read_b(address_t addr, uint8_t *data)
+{
+	if (addr >= 0 && addr < 16) {
+		*data = sfr_data[addr];
+		return 0;
+	}
+
+	return simio_read_b_device(addr, data);
+}
 
 int simio_check_interrupt(void)
 {
diff --git a/simio_device.h b/simio_device.h
index 0a1e5e9..5cd8269 100644
--- a/simio_device.h
+++ b/simio_device.h
@@ -38,6 +38,11 @@ typedef enum {
  *
  *     SFR = (SFR & ~mask) | bits
  */
+#define SIMIO_IE1		0x00
+#define SIMIO_IFG1		0x01
+#define SIMIO_IE2		0x02
+#define SIMIO_IFG2		0x03
+
 uint8_t simio_sfr_get(address_t which);
 void simio_sfr_modify(address_t which, uint8_t mask, uint8_t bits);
 
diff --git a/simio_wdt.c b/simio_wdt.c
new file mode 100644
index 0000000..a53c9a9
--- /dev/null
+++ b/simio_wdt.c
@@ -0,0 +1,272 @@
+/* MSPDebug - debugging tool for MSP430 MCUs
+ * Copyright (C) 2009, 2010 Daniel Beer
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "simio_device.h"
+#include "simio_wdt.h"
+#include "output.h"
+#include "expr.h"
+
+/* WDTCTL flags, taken from mspgcc.
+ *
+ * Watchdog timer password. Always read as 069h. Must be written as 05Ah,
+ * or a PUC will be generated.
+ */
+#define WDTIS0              0x0001
+#define WDTIS1              0x0002
+#define WDTSSEL             0x0004
+#define WDTCNTCL            0x0008
+#define WDTTMSEL            0x0010
+#define WDTNMI              0x0020
+#define WDTNMIES            0x0040
+#define WDTHOLD             0x0080
+#define WDTPW               0x5A00
+
+/* Flags in IE1 */
+#define WDTIE		0x01
+#define NMIIE		0x10
+
+/* Flags in IFG1 */
+#define WDTIFG		0x01
+#define NMIIFG		0x10
+
+struct wdt {
+	struct simio_device		base;
+
+	int				pin_state;
+	int				wdt_irq;
+
+	int				count_reg;
+	int				reset_triggered;
+	uint8_t				wdtctl;
+};
+
+struct simio_device *wdt_create(char **arg_text)
+{
+	struct wdt *w = malloc(sizeof(*w));
+
+	if (!w) {
+		pr_error("wdt: can't allocate memory");
+		return NULL;
+	}
+
+	memset(w, 0, sizeof(*w));
+	w->base.type = &simio_wdt;
+	w->pin_state = 1;
+	w->wdt_irq = 10;
+
+	w->reset_triggered = 0;
+	w->wdtctl = 0;
+	w->count_reg = 0;
+
+	return (struct simio_device *)w;
+}
+
+static void wdt_destroy(struct simio_device *dev)
+{
+	free(dev);
+}
+
+static void wdt_reset(struct simio_device *dev) {
+	struct wdt *w = (struct wdt *)dev;
+
+	w->reset_triggered = 0;
+	w->wdtctl = 0;
+	w->count_reg = 0;
+}
+
+static int parse_int(int *val, char **arg_text)
+{
+	const char *text = get_arg(arg_text);
+	address_t value;
+
+	if (!text) {
+		printc_err("wdt: expected integer argument\n");
+		return -1;
+	}
+
+	if (expr_eval(stab_default, text, &value) < 0) {
+		printc_err("wdt: couldn't parse argument: %s\n", text);
+		return -1;
+	}
+
+	*val = value;
+	return 0;
+}
+
+static int wdt_config(struct simio_device *dev, const char *param,
+		      char **arg_text)
+{
+	struct wdt *w = (struct wdt *)dev;
+
+	if (!strcasecmp(param, "nmi")) {
+		int old = w->pin_state;
+
+		if (parse_int(&w->pin_state, arg_text) < 0)
+			return -1;
+
+		if (w->wdtctl & WDTNMI) {
+			if (((w->wdtctl & WDTNMIES) &&
+				old && !w->pin_state) ||
+			    (!(w->wdtctl & WDTNMIES) &&
+				 !old && w->pin_state))
+				simio_sfr_modify(SIMIO_IFG1, NMIIFG, NMIIFG);
+		}
+
+		return 0;
+	}
+
+	if (!strcasecmp(param, "irq"))
+		return parse_int(&w->wdt_irq, arg_text);
+
+	printc_err("wdt: unknown configuration parameter: %s\n", param);
+	return -1;
+}
+
+static int wdt_info(struct simio_device *dev)
+{
+	struct wdt *w = (struct wdt *)dev;
+
+	printc("Configured WDT IRQ:  %d\n", w->wdt_irq);
+	printc("WDTCTL:              0x__%02x\n", w->wdtctl);
+	printc("NMI/RST# pin:        %s\n", w->pin_state ? "HIGH" : "low");
+	printc("Counter:             0x%04x\n", w->count_reg);
+	printc("Reset:               %s\n",
+	       w->reset_triggered ? "TRIGGERED" : "not triggered");
+
+	return 0;
+}
+
+static int wdt_write(struct simio_device *dev, address_t addr, uint16_t data)
+{
+	struct wdt *w = (struct wdt *)dev;
+
+	if (addr != 0x120)
+		return 1;
+
+	if (data >> 8 != 0x5a)
+		w->reset_triggered = 1;
+
+	w->wdtctl = data & 0xf7;
+	if (w->wdtctl & WDTCNTCL)
+		w->count_reg = 0;
+
+	return 0;
+}
+
+static int wdt_read(struct simio_device *dev, address_t addr, uint16_t *data)
+{
+	struct wdt *w = (struct wdt *)dev;
+
+	if (addr != 0x120)
+		return 1;
+
+	*data = 0x6900 | w->wdtctl;
+	return 0;
+}
+
+static int wdt_check_interrupt(struct simio_device *dev)
+{
+	struct wdt *w = (struct wdt *)dev;
+	uint8_t flags;
+
+	if (!(w->wdtctl & WDTNMI) && !w->pin_state)
+		return 15;
+
+	if (w->reset_triggered)
+		return 15;
+
+	flags = simio_sfr_get(SIMIO_IFG1) & simio_sfr_get(SIMIO_IE1);
+
+	if (flags & NMIIFG)
+		return 14;
+
+	if (flags & WDTIFG)
+		return w->wdt_irq;
+
+	return -1;
+}
+
+static void wdt_ack_interrupt(struct simio_device *dev, int irq)
+{
+	struct wdt *w = (struct wdt *)dev;
+
+	if (irq == 14)
+		simio_sfr_modify(SIMIO_IFG1, NMIIFG, 0);
+	else if (irq == w->wdt_irq)
+		simio_sfr_modify(SIMIO_IFG1, WDTIFG, 0);
+}
+
+static void wdt_step(struct simio_device *dev, uint16_t status_register,
+		     const int *clocks)
+{
+	struct wdt *w = (struct wdt *)dev;
+	int max = 1;
+
+	/* If on hold, nothing happens */
+	if (w->wdtctl & WDTHOLD)
+		return;
+
+	/* Count input clock cycles */
+	if (w->wdtctl & WDTSSEL)
+		w->count_reg += clocks[SIMIO_ACLK];
+	else
+		w->count_reg += clocks[SIMIO_SMCLK];
+
+	/* Figure out the divisor */
+	switch (w->wdtctl & 3) {
+	case 0: max = 32768; break;
+	case 1: max = 8192; break;
+	case 2: max = 512; break;
+	case 3: max = 64; break;
+	}
+
+	/* Check for overflow */
+	if (w->count_reg >= max) {
+		if (w->wdtctl & WDTTMSEL)
+			simio_sfr_modify(SIMIO_IFG1, WDTIFG, WDTIFG);
+		else
+			w->reset_triggered = 1;
+	}
+
+	w->count_reg &= (max - 1);
+}
+
+const struct simio_class simio_wdt = {
+	.name = "wdt",
+	.help =
+"This module simulates the Watchdog Timer+ peripheral. There are no\n"
+"constructor arguments. Configuration parameters are:\n"
+"    irq <irq>\n"
+"        Set the interrupt vector for the WDT interrupt.\n"
+"    nmi <0|1>\n"
+"        Set the state of the NMI/RST# pin.\n",
+
+	.create			= wdt_create,
+	.destroy		= wdt_destroy,
+	.reset			= wdt_reset,
+	.config			= wdt_config,
+	.info			= wdt_info,
+	.write			= wdt_write,
+	.read			= wdt_read,
+	.check_interrupt	= wdt_check_interrupt,
+	.ack_interrupt		= wdt_ack_interrupt,
+	.step			= wdt_step
+};
diff --git a/simio_wdt.h b/simio_wdt.h
new file mode 100644
index 0000000..7600e4c
--- /dev/null
+++ b/simio_wdt.h
@@ -0,0 +1,24 @@
+/* MSPDebug - debugging tool for MSP430 MCUs
+ * Copyright (C) 2009, 2010 Daniel Beer
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#ifndef SIMIO_WDT_H_
+#define SIMIO_WDT_H_
+
+extern const struct simio_class simio_wdt;
+
+#endif